For unsupported statements ROW_NUMBER shows different values depending on previous events

--source include/have_innodb.inc

--disable_abort_on_error

create or replace table t (a tinyint) engine=InnoDB;

backup stage end;

get diagnostics condition 1 @n1 = row_number;

insert into t values (1),(2),(1000);

backup stage end;

get diagnostics condition 1 @n2 = row_number;

select 1;

backup stage end;

get diagnostics condition 1 @n3 = row_number;

select @n1, @n2, @n3;

MariaDB [test]> select @n1, @n2, @n3;

+------+------+------+

| @n1  | @n2  | @n3  |

+------+------+------+

|    0 |    3 |    1 |

+------+------+------+

1 row in set (0.000 sec)